This proposal is intended to examine the central and trigeminal mechanisms of orofacial pain and analgesia in the freely behaving rat. While there has been a vast amount of work dealing with the mechanisms of sensory transmission within the trigeminal nuclear complex, no one theory has been able to define the mechanisms precisely. Nevertheless, ample evidence exists that modulation of sensory messages occur at this primary relay site. Whereas analgesic drugs are in widespread clinical use in the treatment of orofacial pain, few studies have been directed at the trigeminal complex as a possible site of analgesic action. A comparison of the effects of narcotic analgesic drugs (morphine and pentazocine) on evoked potentials, multiple-unit and EEG activity obtained from the trigeminal complex will be made with a non-analgesic drug (pentobarbital). The drug comparisons will be made during the presence and absence of both a noxious and non-noxious tooth pulp stimuli. This study is designed to correlate the bioelectric changes with changes in behavior during sensory stimuli and after drug injection. In order to differentiate the site of morphine action into trigeminal versus more central sites, the technique of analgesic brain stimulation, morphine micro-injection and electrolytic lesioning into either site will be used. The effect of these procedures on both bioelectrical recordings and/or behavior elicited by a tooth pulp stimuli will be ascertained. It is anticipated that upon completion of these studies using the combination of these techniques described and by the use of the freely behaving animal, a more clear understanding of the mechanisms of orofacial pain and analgesia will be available. This can provide for a more rational approach to the clinical management of pain.